The present invention relates to a method for opening and mixing fiber bales in accordance with predetermined proportions in the mixture, wherein the fiber material is removed from the bales by being taken off in individual amounts and the amount removed is measured, and apparatus for carrying out the method.
It is known for fiber material to be removed from bales by being taken off in individual amounts by means of a gripper device for the purposes of putting together fiber mixtures with predetermined proportions therein. The amounts of fibers which are removed from the bales in accordance with the relationship between the constituents of the mixture are collected and measured in an intermediate container which is in the form of a weighing device (U.S. Pat. No. 3,577,599).
In order to achieve a high production output, with the maximum accuracy in regard to maintaining the predetermined proportions in the mixture even when, on the one hand, very small amounts and, on the other hand, amounts which are large in relation thereto have to be taken from the bales to be mixed for the purposes of forming a mixture from different amounts of fibers, it has already been proposed that the amount of fiber which is taken from the bale in each gripping operation should be adapted to the magnitude of the respective constituent of the mixture. Adjustable limit means are associated with the drive arrangement of the gripper for controlling the ratio of the fibers removed from the bales. The limit switch means determines the width that the gripper means is opened and is actuated by a control device which determines the proportions of the constituents of the mixture (U.S. Pat. No. 4,107,820).
This arrangement makes it possible to operate, in the individual fiber supply stations which contain the respective constituents of the mixture, in accordance with the magnitude of the respective proportions to be supplied thereby with the gripper means set to a width of opening which is adapted to the respective constituent of the mixture. By adjustment of the limit means, the gripper means is set to a wide width of opening when dealing with fiber which forms a large proportion of the mixture while the gripper means is set to a small width of opening when dealing with a small constituent. If there is a plurality of fiber supply stations and if such stations are required to supply different amounts of fiber to form the respective proportions of the mixture, the number of limit means corresponds to the number of constituents of the mixture or fiber supply stations so that each fiber supply station has associated therewith a different width of opening of the gripper device which is adapted to the respective constituent of the mixture at that station. As an alternative, in accordance with the known proposal, the width of opening can be limited to two widths if there is considerable difference only between the constituents at two fiber supply stations while if there are other constituents, those other constituents are close to the above-mentioned two constituents. This system, however, also retains the principle of operating with a wide width of opening in relation to a fiber supply station with a constituent forming a large proportion of the mixture, and with a small width of opening when operating at a fiber supply station giving a constituent forming a small proportion of the mixture.
However, with this mode of operation, it may occur that when removing large amounts of fiber with the gripper means set to a correspondingly wide width of opening at a fiber supply station, a large amount of fiber may again be taken from a bale although the constituent of the mixture has almost reached its desired weight. In this case, the actual weight of the constituent will exceed the desired weight to an inadmissible extent.